Based on some calculations I did today, I am offering
an original rule of thumb (as far as I know). Regarding
a coax choke, when deciding how many turns of coax to put
on a 2 liter pop bottle at two turns per inch, one needs
to avoid the self-resonant frequency. So don't put more
turns on the choke than the number of meters in a wavelength,
e.g. no more than 20 turns on 20m, no more than 6 turns on
6m. Backup calculations will be published on my web page.
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73, Cecil http://www.qsl.net/w5dxp